The more radiation therapy you receive, the more likely it is you’ll develop a second cancer caused by that radiation, according to a document[PDF] released by the American Cancer Society, which admits that certain organs such as the breast and thyroid are more prone to developing a second cancer.

This information is followed by a new study which found that second cancers in Americans have increased a whopping 300 percent since the 1970s, all of which are a completely new type of cancer and not a reoccurrence of an old cancer.

The study also found that first cancers have spiked 70 percent over the last 45 years, highlighting the burgeoning profitability of an industry that shows no signs of slowing down as capital gains from cancer drugs reached the $100 billion mark last year.

Radiation, which may damage DNA, is believed to be responsible for 1.5 percent of cancer in the United States, and that’s not just from cancer therapy treatments but also from other sources of radiological imaging such as mammograms and coronary artery and CT scans, the latter of which delivers 100 to 500 times the radiation of an ordinary X-ray.

“For every 1,000 people undergoing a cardiac CT scan, the radiation adds one extra case of cancer to the 420 that would normally occur,” according to The New York Times.

Children exposed to radiation much more likely to develop breast cancer

Children who have received radiation therapy as a cancer treatment are much more likely to develop breast cancer later on in life. Age at the time of radiation plays a factor as the “therapy” affects the development of other tumors including lung and thyroid cancer, gastrointestinal and stomach cancer and bone sarcoma.

If a patient receives chemotherapy and radiation, their risk for developing some type of second cancer soars even higher.

The longer you receive treatment involving alkylating agents, as well as the higher the dose, the more likely you are to develop a second cancer, with the risk for leukemia rising about two years following treatment and peaking between five and ten years, after which the risk reportedly dwindles.

Second cancers caused by chemo drugs are “hard to treat and have a poor outcome”

Though not as risky, other chemotherapy drugs can also cause second cancers. Chemo drugs cisplatin and carboplatin act similarity to alkylating agents in the way they attack cancer cells, in turn also increasing certain types of leukemia that are difficult to treat and often have a poor outcome.

If cisplatin or carboplatin are given in combination with radiation, the risk for developing leukemia rises.

Topoisomerase II inhibitors, a class of chemo drugs that inhibit cells from being able to repair DNA, also contribute to the risk of developing leukemia, particularly AML, which develops much sooner (within two to three years) after treatment compared with alkylating agents.

Drugs in this class include:

• Etoposide (VP-16)
• Teniposide
• Mitoxantrone (Novantrone)

Another class of chemo drugs called anthracyclines, which are also topoisomerase II inhibitors, cause leukemia as well but aren’t as risky as the other drugs mentioned.